1. Field of the Invention
The present invention relates to an electron gun for a CRT (cathode ray tube), and, more particularly, to an electrode of an electron gun embedded in a bead glass, and an electron gun including the electrode.
2. Description of the Related Art
In a typical electron gun for a CRT, electron beam passing holes in electrodes are arranged in-line, i.e., have centers lying on a straight line, and the electron gun including the electrodes is installed in a neck of the CRT. The electrodes have various shapes, such as a plate, a cylinder, and a cup, and are coaxially arranged and separated by spacers. Opposite edges of the electrodes are fixedly supported by bead glass.
Fixing the electrodes to support bead glasses is referred to as a beading process. In the beading process, at least one pair of supports along an edge of an electrode is embedded in the bead glass while the bead glass is half melted with a flame. xe2x80x9cHalf-meltedxe2x80x9d means the bead glass is sufficiently softened with heat to flow viscously in response to applied pressure, but the bead glass is not fully melted, i.e., is not liquid. There have been many attempts to improve the degree of bonding of the bead glass to the support that is embedded. The technology of making the structure of a support to be embedded in the bead glass of electrodes is complicated, with the goal that the supports not be easily separated from the bead glass. However, when the structure of the support is complex, cracks occur in the bead glass in the embedding step, causing deterioration of an electron gun.
To solve this problem, according to Japanese Patent Publication No. 2000-348637, the structure of at least one of a plurality of support pairs, which are not plate shaped but three-dimensional, are installed parallel to one another on the electrodes. The structure is kept simple to reduce stress applied to the bead glass so that cracks generated in the embedding step can be reduced. However, this technology has a limit since it does not improve the structure of the support that is embedded in the bead glass. In other words, in the electrodes, the support of each electrode has a pair of protrusions to be embedded in the bead glass and the protrusions are inwardly bent and face each other. In the support having a simplified shape, the number of branches are reduced but the bent shape itself is not changed.
In a complicated electrode support or inwardly bent electrode support, since the bead glass in a half-melted state is injected between the embedding protrusions, the viscous half-melted bead glass is not smoothly injected.
When a bead glass having a beveled outside corner is used to support electrodes, and the beveled portion and the outer one of embedding protrusions close to each other, support strength of the bead glass is weakened. To avoid this weakness, the bead glass is made thicker with the result that the electrode assembly is not compact.
FIG. 1 shows an electrode 10 supported by a bead glass. Referring to FIG. 1, in a typical electrode of an electron gun for a CRT, three electrode beam passing holes 12 for electron beams respectively producing red, green, and blue light, are located in-line at a central portion of the electrode. A support at each of upper and lower edges of the electrode is embedded in a bead glass 14. The bead glass 14 has a thickness T between surfaces generally parallel to a line joining the centers of the electron beam passing holes 12. The bead glass 14 includes beveled surfaces 14a, oblique to the surfaces between which the thickness is measured. To join the supports and the bead glass, a plurality of electrodes having plate, cylinder, and cup shapes, and arranged parallel to one another, are fixed in a jig by interposing spacers between the electrodes. Then, the bead glass in a half melted state is pressed toward a portion of the electrode at the support. Thus, the support is inserted into and fixed by the bead glass so that the electrodes are supported.
When the support of the electrode is pressed into the half melted bead glass, the bead glass flows between embedding protrusions 16a and 16b of the support, as indicated by arrows in FIG. 1. Since the bead glass is not completely melted and exhibits a certain degree of viscosity, the bead glass provides a predetermined resistance to the embedding protrusions 16a and 16b. The bead glass may not be sufficiently inserted into an inner curved portion 18 between the embedding protrusions 16a and 16b. If an excess pressure is applied to insert the half melted bead glass into the internal curved portion 18, cracks are generated. On the other hand, a gap between the bead glass and the electrode is produced if the half melted bead glass is not sufficiently injected between the protrusions 16a and 16b. The gap supports the flow of a leakage current in the electron gun.
Also, as shown in FIG. 1, the thickness T of the bead glass 14 cannot be reduced since a minimum distance i is required between the beveled portion 14a of the bead glass and the outer embedding protrusion 16b of the support to ensure adequate strength of the bead glass.
To solve the above-described problems, it is an object of the present invention to provide an electron gun in which the structure of an embedding portion of an electrode is improved, preventing cracking in a bead glass during the beading process and minimizing twisting in a gap between the bead glass and an electrode support.
It is another object of the present invention to provide an electron gun in which a gap between the bead glass and the electrode is minimized and the degree of bonding is improved so that arcing resistance inside a CRT is improved and the leakage current is prevented.
It is yet another object of the present invention to provide an electron gun for a CRT in which the size of the bead glass is reduced while maintaining embedding strength by changing the shape of an embedding protrusion of an electrode support.
To achieve the above object, an electron gun for a CRT comprises a plurality of electrodes arranged sequentially and having a plurality of electron beam passing holes, and a pair of bead glasses separated from and parallel to each other, supporting the plurality of electrodes of the electron gun, wherein at least one of the electrodes includes at least two electrode supports respectively embedded in the respective bead glasses, each electrode support comprising first and second embedding protrusions embedded in one of the bead glasses, the first embedding protrusion protruding further from the electrode than the second embedding protrusion.
Each bead glass includes a first planar surface and a second planar surface oblique to the first planar surface and generally parallel to a straight line tangent to the first and second embedding protrusions
It is preferred in the present invention that an angle between the straight line tangent to both the first and second embedding protrusions and a line connecting the electron beam passing holes is within a range of 15xc2x0 through 45xc2x0.
It is preferred in the present invention that the first and second protrusions are separated by a width varying with distance from the electrode and include an inlet where the bead glass flows between the first and second embedding protrusions, and the inlet has a width at least 95% of a maximum width between the first and second embedding protrusions.
It is preferred in the present invention that the first embedding protrusion is closer to a center portion of the electrode than the second embedding protrusion.
It is preferred in the present invention the electrode has a depth as well as a height and includes an auxiliary electrode support embedded in one of the bead glasses and located on a surface of the electrode, facing the bead glass.
An electron gun according to the invention includes a plurality of electrodes arranged sequentially and having a plurality of electron beam passing holes, and first and second bead glasses separated from and parallel to each other, supporting the plurality of electrodes of the electron gun, wherein at least one of the electrodes includes at least first and second electrode supports respectively embedded in the first and second bead glasses, the first electrode support comprising a central embedding protrusion embedded in the first bead glass and first and second embedding protrusions on opposite sides of the central embedding protrusion and embedded in the first bead glass, the central protrusion protruding farther from the electrode than the first and second embedding protrusions.
It is preferred in the present invention that the auxiliary electrode support comprises at least two auxiliary embedding protrusions and at least one of the auxiliary embedding protrusions extends further from the electrode than the other auxiliary embedding protrusion.